Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:2.4.2.8 (hypoxanthine-guanine phosphoribosyltransferase)
 2,527 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Tiazofurin (2-beta-D-ribofuranosylthiazole-4-carboxamide, NSC 286193), a selective inhibitor of the activity of IMP dehydrogenase (EC 1.1.1.205), the rate-limiting enzyme of de novo GTP biosynthesis, provided in end stage leukemic patients a rapid decrease of IMP dehydrogenase activity and GTP concentration in the blast cells and a subsequent decline in blast cell count. Sixteen consecutive patients with end stage acute nonlymphocytic leukemia or myeloid blast crisis of chronic granulocytic leukemia were treated with tiazofurin. Allopurinol was also given to inhibit xanthine oxidase activity to decrease uric acid excretion and to elevate the serum concentration of hypoxanthine, which should competitively inhibit the activity of hypoxanthine-guanine phosphoribosyltransferase (EC 2.4.2.8), the salvage enzyme of guanylate synthesis. Assays of IMP dehydrogenase activity and GTP concentration in leukemic cells provided a method to monitor the impact of tiazofurin and allopurinol and to adjust the drug doses. In this group of patients with poor prognosis, five attained a complete hematological remission and one showed a hematological improvement. A marked antileukemic effect was seen in two other patients. All five evaluable patients with myeloid blast crisis of chronic granulocytic leukemia reentered the chronic phase of their disease. Five patients with acute nonlymphocytic leukemia were refractory to tiazofurin and three were unevaluable for hematological effect because of early severe complications. Responses with intermittent 5- to 15-day courses of tiazofurin lasted 3-10 months. Tiazofurin had a clear antiproliferative effect, but the pattern of hematological response indicated that it appeared to induce differentiation of leukemic cells. In spite of toxicity with severe or life-threatening complications in 11 of 16 patients, tiazofurin was better tolerated in most patients than other antileukemic treatment modalities and provided a rational, biochemically targeted, and biochemically monitored chemotherapy which should be of interest in the treatment of leukemias and as a paradigm in enzyme pattern-targeted chemotherapy.
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PMID:Biochemically directed therapy of leukemia with tiazofurin, a selective blocker of inosine 5'-phosphate dehydrogenase activity. 256 8

Some of the current critical issues in the tiazofurin treatment of end-stage leukemia were presented and discussed. 1. Tiazofurin infusions (daily X 10 to 15) provided remissions in 50% of end-stage leukemic patients. The remissions, of 1 to 10 months' duration, varied from antileukemic effect or hematologic improvement to complete response and complete remission. The total survival of the responding patients was from about 1 to 15 months. 2. Our administration of tiazofurin in a 60-min infusion by pump decreased the incidence and severity of toxicity. 3. It was shown that tiazofurin dose does not need to be escalated at each relapse. Depending on the biochemical and hematological response in this novel protocol, 2,200 to 4,400 mg/m2 tiazofurin appeared to be sufficient to provide remissions. 4. A new role was identified for allopurinol, originally given to decrease uric acid in the plasma. Allopurinol markedly increased plasma hypoxanthine concentrations which competitively inhibited the activity of the salvage enzyme, guanine phosphoribosyltransferase, in the blast cells. Thus, the elevated hypoxanthine plasma levels inhibited guanine salvage. To maintain high hypoxanthine levels allopurinol (100 mg) was given every 4 to 6 hr. This provided combination chemotherapy with tiazofurin which inhibited IMP dehydrogenase activity and blocked the de novo biosynthesis of guanylates in the blast cells. 5. Preliminary evidence was obtained in the patients that tiazofurin induced differentiation of the bone marrow. Recent studies also showed that tiazofurin down-regulated the expression of the c-Ki-ras oncogene in K562 erythroleukemic cells. Therefore, tiazofurin treatment provides an impact by chemotherapy, induced differentiation, and, if applicable, through down-regulation of the ras oncogene. 6. Novel aspects of tiazofurin treatment include rational targeting and a continuously monitored trial by measurement of the activity of IMP dehydrogenase and of GTP and TAD concentrations in blast cells and of tiazofurin and hypoxanthine in plasma. 7. Since tiazofurin has not yet achieved lasting remissions in patients nor terminal differentiation of leukemic cells it probably will be advantageous to combine tiazofurin with other drugs to provide synergism. In preclinical tissue culture studies in HL-60 cells synergy was observed with retinoic acid. This may be of interest because retinoic acid also caused differentiation and down-regulation of the myc oncogene.
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PMID:Critical issues in chemotherapy with tiazofurin. 269 55

The adenine phosphoribosyltransferase (APRTase) and hypoxanthine-guanine phosphoribosyltransferase (HGPRTase) activities from promastigotes of Leishmania donovani have been purified to homogeneity using ammonium sulfate precipitation, DEAE-cellulose exclusion, and either AMP-agarose (APRTase) or GTP-agarose (HGPRTase) affinity chromatography. The specific activities of the affinity-purified APRTase and HGPRTase fractions were 326-fold and 1341-fold greater than those in the 40-80% ammonium sulfate precipitate, respectively. The purified APRTase migrated as a single band on sodium dodecyl sulfate (SDS) polyacrylamide gels with a size of 29 kDa, while HGPRTase was also determined to be homogeneous by SDS gel electrophoresis with a size of 24 kDa. In addition, a mutant cell line, APPB2, partially deficient in APRTase activity, still contained quantities of purifiable APRTase protein, while a clonal secondary derivative of the APPB2 cell line that is completely deficient in APRTase activity, APPB2-640A3, failed to express purifiable APRTase protein. The homogeneous enzymes possessed apparent Km values for their nucleobase substrates between 2.0 and 5.0 microM, and both enzymes were inhibited by their immediate or ultimate reaction endproducts, APRTase by AMP and PPi and HGPRTase by GMP, GTP, and PPi. The generation of homogeneous preparations of APRTase and HGPRTase protein will serve as a prerequisite for the generation of immunological and molecular biological probes to analyze the leishmanial phosphoribosyltransferases.
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PMID:Purification and characterization of the adenine phosphoribosyltransferase and hypoxanthine-guanine phosphoribosyltransferase activities from Leishmania donovani. 270 89

The metabolic pathways of pterin de novo synthesis, interconversion and salvage which lead to the tetrahydrobiopterin cofactor of phenylalanine 4-monooxygenase, tyrosine 2-monooxygenase and tryptophan 5-monooxygenase are reviewed and data on the enzymes which catalyze the individual steps are presented. Analogies drawn between the inborn errors of tetrahydrobiopterin production and the Lesch-Nyhan syndrome, in which purine salvage is deficient, are used as a basis for the hypothesis that the neurological manifestations of the Lesch-Nyhan syndrome are due to neurotransmitter imbalance which stems from an imbalance of the aromatic amino acid monooxygenase activities which are themselves due to impaired pterin biosynthesis. The latter arises because, in the absence of the hypoxanthine phosphoribosyltransferase catalyzed purine salvage pathway, the supply of GTP for the GTP cyclohydrolase reaction, which is the first reaction on the pterin de novo synthesis pathway, is reduced. It is proposed that the different aromatic amino acid monooxygenases are differentially affected by this constrained pterin production. The activities of those most directly related to the quantal production of the cerebral neurotransmitters dopamine, norepinephrine and 5-hydroxytryptamine are affected whereas liver phenylalanine 4-monooxygenase activity is not overtly impaired. The results of different lines of research which support this concept are cited, as is direct evidence for a selective reduction of dopamine production in the basal ganglia of patients with the Lesch-Nyhan syndrome. It is proposed that lack of GMP for functions, other than its role in pterin de novo synthesis, accounts for the features of the Lesch-Nyhan syndrome which do not occur when only tetrahydrobiopterin production is deficient as in the inborn errors of tetrahydrobiopterin synthesis.
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PMID:Defects of tetrahydrobiopterin synthesis and their possible relationship to a disorder of purine metabolism (the Lesch-Nyhan syndrome). 286 76

The hypothesis was tested that the increased IMP dehydrogenase activity in human myelocytic leukemic cells, and along with it guanylate biosynthesis, might be a sensitive target to chemotherapy by tiazofurin. 1. IMP dehydrogenase activity in normal leukocytes was 3.1 +/- 0.5 (means +/- S.E.) nmol/hr/mg protein and in leukemic cells it was elevated 15- to 41-fold. The activity of guanine phosphoribosyltransferase in normal leukocytes was 389 +/- 27 nmol/hr/mg protein and in the leukemic cells it increased 2.8- to 6.8-fold. 2. IMP dehydrogenase was purified 4,900-fold to homogeneity from rat hepatoma 3924A with a yield of 30%. The kinetic properties of the hepatoma enzyme were similar to those of the enzyme in human myelocytic leukemic blast cells because of the similarity of the Km's for IMP (23 microM), NAD (44 and 65 microM); the Ki for TAD was 0.1 microM in both enzymes. 3. There was a selectivity of the in vitro response to tiazofurin in human normal and leukemic leukocytes. When labeled tiazofurin was incubated with leukocytes from normal, healthy volunteers and from leukemic patients, the leukemic leukocytes made 20- to 30-fold more TAD and the GTP content decreased as compared to normal leukocytes. This procedure proved to be a suitable predictive test in a clinical setting because patients with positive tests responded to tiazofurin whereas those with negative ones did not. 4. The National Cancer Institute approved a chemotherapeutic phase I/II trial which concentrates on treatment of refractory acute myelocytic leukemia. Tiazofurin is infused in a 60-minute period with a pump to insure uniform delivery. A novel aspect of the trial was that it was directed primarily by the biochemical impact of tiazofurin on IMP dehydrogenase activity and GTP concentration and the tiazofurin doses were to be adjusted accordingly. Patients received allopurinol as a routine precaution against possible accumulation of uric acid in the kidney. 5. In the first eight patients, there was one complete remission, two entered the chronic phase, two entered into partial remission, one did not respond, and two were not evaluable. In the five patients who responded, there was a rapid, profound decrease in IMP dehydrogenase activity of the blast cells and a gradual decline in GTP concentrations. The blast cell count followed the decrease in the GTP concentration. The white blood cell count was largely preserved. 6. Bone marrow aspirates and peripheral blood samples showed that with tiazofurin treatment there was an induced differentiation of the myelocytes.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:Enzyme-pattern-targeted chemotherapy with tiazofurin and allopurinol in human leukemia. 290 68

This paper compares erythrocyte nucleotide levels in patients with eight different inherited purine or pyrimidine enzyme defects identified amongst a variety of patients referred predominantly for investigation of severe neurological abnormalities, or immunodeficiency syndromes. Characteristic nucleotide patterns were identified only in the six disorders (four involving purine and two pyrimidine metabolism) where there was clinical evidence of cellular toxicity. They were frequently related to the accumulation of abnormal metabolites in body fluids. These erythrocyte studies have demonstrated the following. 1. ATP depletion is not an invariable feature of adenosine deaminase (ADA) deficiency, but the accumulation of the deoxyribonucleotides dATP, or dGTP, is diagnostic of ADA, or purine nucleoside phosphorylase (PNP) deficiency, respectively. The early accumulation of dATP in foetal blood is a valuable aid to prenatal diagnosis of ADA deficiency. 2. GTP depletion appears to reflect the degree of CNS involvement in hypoxanthine-guanine phosphoribosyltransferase and PNP deficiency, as well as PP-ribose-P synthetase superactivity. Other diagnostic changes involving increased pyrimidine sugars and increased or decreased NAD levels, or ZTP in Lesch Nyhan erythrocytes, show no consistent correlation with the clinical manifestations. 3. These altered nucleotide levels afford a novel means for carrier detection of the X-linked defect associated with aberrant PP-ribose-P synthetase activity, where no other test is yet available. Measurement of erythrocyte nucleotide levels thus provides a simple and rapid aid to diagnosis and may sometimes be essential for determining prognosis, carrier detection, or monitoring therapy. These characteristic 'fingerprints' may give some insight into the mechanism by which the abnormal gene product produces disease. Such grossly altered nucleotide levels could also result in loss of erythrocyte flexibility, increased destruction and hence the anaemia, or other clinical manifestations, observed in some disorders.
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PMID:Altered erythrocyte nucleotide patterns are characteristic of inherited disorders of purine or pyrimidine metabolism. 337 Aug 20

Tiazofurin, a C-nucleoside, was cytotoxic in hepatoma 3924A cells grown in culture with an LC50 = 7.5 microM. In the culture, a closely linked dose-related response of tumor cell-kill and depletion of GTP pools was observed after tiazofurin treatment. In rats carrying subcutaneously transplanted hepatoma 3924A solid tumors, a single intraperitoneal injection of tiazofurin (200 mg/kg) caused a rapid inhibition of IMP dehydrogenase (EC 1.2.1.14) activity and depleted GDP, GTP, and dGTP pools in the tumor; concurrently, the 5-phosphoribosyl 1-pyrophosphate (PRPP) and IMP pools expanded 8- and 15-fold, respectively. Tiazofurin decreased tumoral IMP dehydrogenase activity and dGTP pools in a dose-dependent manner over a range of 50-200 mg/kg; by contrast, the depletion of GTP and the accumulation of IMP and PRPP pools were near maximum at 50 mg/kg. The increase in PRPP pools may be attributed to an inhibition by IMP of the activity of hypoxanthine-guanine phosphoribosyltransferase (EC 2.4.2.8). The IMP dehydrogenase activity and the pools of ribonucleotides returned to the normal range by 24-48 h after the single injection of tiazofurin. However, the markedly depleted dGTP pools remained low for 72 h. Tiazofurin treatment resulted in significant anti-tumor activity in rats inoculated with hepatoma 3924A. The decrease in GTP levels and particularly the sustained depletion in the dGTP pools may explain, in part at least, the chemo-therapeutic action of tiazofurin on hepatoma 3924A. This is the first report showing that a marked therapeutic response was achieved against rapidly growing hepatoma 3924A by treatment with a single anti-metabolite.
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PMID:Modulation of IMP dehydrogenase activity and guanylate metabolism by tiazofurin (2-beta-D-ribofuranosylthiazole-4-carboxamide). 614 52

The isolation and characterization of a mutant mouse T-cell lymphoma (S49) with altered purine metabolism is described. This mutant, AU-100, was isolated from a mutagenized population of S49 cells by virtue of its resistance to 0.1 mM 6-azauridine in semisolid agarose. The AU-100 cells are resistant to adenosine mediated cytotoxicity but are extraordinarily sensitive to killing by guanosine. High performance liquid chromatography of AU-100 cell extracts has demonstrated that intracellular levels of GTP, IMP, and GMP are all elevated about 3-fold over those levels found in wild type cells. The AU-100 cells also contain an elevated intracellular level of pyrophosphoribosylphosphate (PPriboseP), which accounts for its resistance to adenosine. However AU-100 cells synthesize purines de novo at a rate less than 35% of that found in wild type cells. Furthermore, the intact cells of this mutant S49 cell line cannot efficiently incorporate labeled hypoxanthine into nucleotides since the salvage enzyme HGPRTase is inhibited in situ. The AU-100 cell line was found to be 80% deficient in adenylosuccinate synthetase, but these cells are not auxotrophic for adenosine or other purines. The significant alterations in the control of purine de novo and salvage metabolism caused by the defect in adenylosuccinate synthetase are mediated by the resulting increased levels of guanosine nucleotides.
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PMID:Abnormal regulation of purine metabolism in a cultured mouse T-cell lymphoma mutant partially deficient in adenylosuccinate synthetase. 615 49

The mechanism of action of acivicin and tiazofurin was compared in hepatoma 3924A. The results were evaluated by assessing the impact of these drugs on primary targets, the activities of key enzymes, and on secondary and tertiary targets, the concentrations of pools of ribonucleotides and deoxyribonucleotides. The action of acivicin entails inhibition and inactivation of the key enzymes of glutamine utilization in the biosynthesis of purines and pyrimidines. As a result, the GTP and CTP pools were markedly depleted, whereas those of ATP and UTP were unaffected. Acivicin also markedly decreased the concentrations of all 4 deoxynucleoside triphosphates. The nucleotide pools returned to normal or near normal range within 2 to 3 days after a single acivicin injection. The pharmacologic targets of acivicin in anticancer chemotherapy include prominently the activities of glutamine-utilizing enzymes and the pools of GTP and CTP and all 4 dNTP's. These biochemical targets also serve as indicators of acivicin action in cancer cells. The action of tiazofurin in hepatoma cells entails the primary target, IMP dehydrogenase. The subsequent effects include marked enlargement of IMP and PRPP pools and depletion of the pools of GDP and GTP. The increased IMP concentration selectively inhibited the activities of hypoxanthine-guanine phosphoribosyltransferase, but did not affect that of adenine phosphoribosyltransferase. The markedly decreased GTP pool de-inhibited the activity of AMP deaminase which permitted the channeling of AMP to IMP. An important indicator of tiazofurin action is the prolonged depletion of dGTP pools and similar but less pronounced declines in the pools of dCTP and dATP. In contrast, dTTP pools were increased. The crucial biochemical targets and indicators of tiazofurin action in sensitive cancer cells include inhibition of IMP dehydrogenase, a decrease in the concentrations of GDP, GTP, dGTP, dCTP, dATP and marked rise in the pools of IMP, PRPP and dTTP. Measurements of the molecular targets and indicators of drug action should be helpful in identifying cancer cells and tissues sensitive or resistant to the action of acivicin or tiazofurin. Identification of the targets and indicators should also be helpful in the design of frequency of administration of the drugs in combatting animal and human neoplasia.
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PMID:Control of enzymic programs and nucleotide pattern in cancer cells by acivicin and tiazofurin. 620 92

The hepatic metabolism of hypoxanthine was investigated by studying both the fate of labelled hypoxanthine, added at micromolar concentrations to isolated rat hepatocyte suspensions, and the kinetic properties of purified hypoxanthine/guanine phosphoribosyltransferase from rat liver. More than 80% of hypoxanthine was oxidized towards allantoin; less than 5% of the label was incorporated into the purine mononucleotides, and a similar proportion appeared transiently in inosine. The maximal velocity of oxidation (approx. 750nmol/min per g of cells) was in close agreement with the known activity of xanthine oxidase in liver extracts. In contrast, the maximal velocity of the incorporation of labelled hypoxanthine into mononucleotides reached only 30nmol/min per g of cells, compared with an activity of hypoxanthine/guanine phosphoribosyltransferase, measured at substrate concentrations analogous to those prevailing intracellularly, of 500nmol/min per g of cells. Hypoxanthine incorporation into the mononucleotides was decreased by allopurinol, anoxia and ethanol, despite inhibition of its oxidation under these conditions; it was increased by incubation of the cells in supraphysiological concentrations of Pi. Allopurinol and anoxia decreased the concentration of phosphoribosyl pyrophosphate inside the cells by respectively 40 and 60%, ethanol had no effect on the concentration of this metabolite and Pi increased its concentration up to 10-fold. The kinetic study of purified hypoxanthine/guanine phosphoribosyltransferase showed that a mixture of ATP, IMP, GMP and GTP, at the concentrations prevailing in the liver cell, decreased the V max. of the enzyme 6-fold, increased its Km for hypoxanthine from 1 to 4 microM and its Km for phosphoribosyl pyrophosphate from 2.5 to 25 microM. In the presence of 5 microM-hypoxanthine and 2.5 microM-phosphoribosyl pyrophosphate, the mixture of nucleotides inhibited the activity of purified hypoxanthine/guanine phosphoribosyltransferase by 95%. It is concluded that this inhibition results in a limited participation of hypoxanthine/guanine phosphoribosyltransferase in the control of the production of allantoin by the liver.
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PMID:Metabolism of hypoxanthine in isolated rat hepatocytes. 620 48


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